BIR stands for 'Baculovirus Inhibitor of apoptosis protein Repeat'. It is found repeated in inhibitor of apoptosis proteins (IAPs), and in fact it is also known as IAP repeat. These domains characteristically have a number of invariant residues, including 3 conserved cysteines and one conserved histidine that coordinate a zinc ion. They are usually made up of 4-5 alpha helices and a three-stranded beta-sheet. BIR is also found in other proteins known as BIR-domain-containing proteins (BIRPs), such as Survivin (Swiss:O15392) [2].

1: An apoptosis-inhibiting gene from a nuclear polyhedrosis virus encoding a polypeptide with Cys/His sequence motifs. Birnbaum MJ, Clem RJ, Miller LK; J Virol 1994;68:2521-2528. PMID:8139034

2: Inhibitor of apoptosis proteins and their relatives: IAPs and other BIRPs. Verhagen AM, Coulson EJ, Vaux DL; Genome Biol 2001;2:REVIEWS3009. PMID:11516343